Why I'm staying invested in overvalued market: Expert

August is a traditionally tough month for stocks, but for now investment pro Jack Ablin is staying invested in the market despite feeling that it is as much as 25 percent overvalued.

"Valuation is not by itself a timing tool so we can get a market that's expensive and keeps getting expensive," the chief investment officer of BMO Private Bank said in an interview with CNBC's "Power Lunch" on Monday.

"Generally what we like to do is stay with momentum, stay with a good thing, as long as it keeps going."

Brendan McDermid | Reuters

Trader on the floor of the New York Stock Exchange.

Ablin said that 25 percent overvaluation can also be cut a little slack because he looks at prices relative to sales, and profits are expanding.

"I don't view it necessarily as a threat. It can be a threat, maybe a 10 to 15 percent threat, but it is in no uncertain terms a headwind. There's no doubt that that's what's really preventing the market from going higher this year."